Microsoft on Monday night will debut a new television advertising campaign hoping to convince consumers to upgrade their older PCs to ones running Windows 7.

The ads will run on ABC, CBS and NBC starting in the 8 p.m. time slot. One of them is available now on YouTube.

As first reported by Todd Bishop of GeekWire, the ads will be the latest incarnation of the "I'm a PC" campaign that ran more than two years ago, but will target consumers already using Microsoft Windows.

"The ads feature real couples who thought their old (4+ years) PC was 'good enough' being surprised to find a Personal PC store built out in their homes," Microsoft said in a statement.

"Good enough" is a phrase often used by analysts to describe a developer's difficulty getting customers to upgrade to the newest software when older versions are sufficient for their needs.

"Our goal is to showcase the wide world of Windows PCs to show people they can get a highly customized and productive PC that may surprise them with its stylish look and feel," Microsoft said.

That may be a tough job, said Michael Cherry, an analyst with Directions on Microsoft, a Kirkland, Wash. research firm that covers only Microsoft. And not simply because of the "good enough" problem.

"At the end of the day, this is not even about 'good enough' anymore," said Cherry. "There's a whole bunch of other things happening."

From Cherry's perspective, Microsoft not only competes against itself -- Windows XP or Vista versus Windows 7, for instance -- but also against other technologies that consumers may value higher than a new PC.

"I have X number of dollars I can spend on things, and once the PC was one of those things," said Cherry. "But now people are saying, 'I like these new smartphones, I like these new tablets.' Microsoft is trying to get the PC back on that wish list."

Windows revenues from consumers are tightly tied to new PC purchases, which have dramatically slowed. In the first quarter of 2011, Windows revenues fell by 4%; Microsoft attributed the slide to a drop in global PC shipments, which according to market research firms IDC and Gartner, dropped by 3.2% and 1.1%, respectively.